1. Field of Invention
The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure concerns axially stabilizing submersible pump stators with mechanical anchoring.
2. Description of Prior Art
Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the wellbore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used in this application employs an electrical submersible pump (ESP). ESPs are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power may be supplied to the pump motor via a power cable. Typically, the pumping unit is disposed within the well bore just above where perforations are made into a hydrocarbon producing zone. This placement thereby allows the produced fluids to flow past the outer surface of the pumping motor and provide a cooling effect.
FIG. 1 provides in side view an electrical submersible pump (ESP) system used for the production of wellbore fluids produced from a hydrocarbon borehole. Here, the ESP system 20 is shown disposed in a wellbore 5, where the wellbore 5 is lined with casing 11. The wellbore 5 is formed through a formation 7 and intersects a hydrocarbon producing zone. Perforations 9 are formed through the casing 11 and into the surrounding formation 7, thereby allowing for hydrocarbons entrained in the formation 7 to enter into the wellbore 5. A produced hydrocarbon, is shown exiting the perforations 9 and into the wellbore 5 as arrows A. The ESP system 20 comprises a pump motor 22 at its lowermost section. Adjacent the pump motor 22 is the seal section 24. The seal section 24 is responsive to ambient pressure and transfers the ambient pressure to the internal portions of the pump system thereby substantially equalizing pump system internal pressure with ambient to minimize the pressure differential across the pump system seals. A fluid inlet 26 is provided on a gas separator 28 and configured to receive wellbore production fluid therein for delivery to the pump 29. The pressurized wellbore fluid exiting the pump 29 flows into production tubing 30 for delivery to the surface where is then transmitted for further refinement. Gas removed in the separator is typically discharged from the pumping system and back into the wellbore where it flows to the wellhead.
Motors for electrical submersible pump systems are typically formed by stacking a series of stator laminations inside a pump motor housing. Grooves are formed within the housing at the top and bottom terminal ends of lamination stack. The grooves are configured to receive a snap ring, where the snap ring inner diameter extends into the pump motor from the housing inner diameter. Forming the motor typically comprises inserting the snap ring located at the bottom of the housing, then adding the lamination stack within the housing. The laminations are then compressed, with a press or some other mechanical device; while the laminations are still under compression the stop snap ring is inserted. After the pressure on the lamination stack is released, the stack will slightly spring back and exert an axial force on both top and bottom snap rings, where the opposing force is in opposite directions. This force on the snap rings will slightly stretch the housing along its length. The residual force in the lamination stack and the snap rings locks the laminations into place thereby preventing lamination spin during motor operation.
The ESP pump motors also comprise a rotor attached to a pump motor shaft. The rotor also consists of corresponding rotor laminations. The stator lamination stack and the rotor lamination stack include openings that axially run along the length of the motor, wherein the openings contain wires, or other electrical conducting elements that form corresponding coils in each of the rotor and stator lamination stack. Typically the coil in the stator lamination stack is energized to form an electrical field that through electromagnetic forces produces a rotation in the rotor stack and thus correspondingly rotates the pump motor shaft.